Coinjection molding of preforms for use in blow molding is known in the prior art. The formation of such containers is described in detail, for example, in Applicant's U.S. Pat. No. 4,550,043. Both single material preforms and multi-material preforms have been injection molded in prior art multi-cavity molds, which may have as many as 96 cavities, into which the material, from which the preforms are to be formed, is injected simultaneously thereby to simultaneously produce a preform in each of the cavities.
FIG. 1 is a diagrammatic illustration of a prior art mold in which two different materials are sequentially and contiguously supplied to a plurality of cavities through a common manifold system. The manifold system of FIG. 1 and a process of using the system are disclosed in Applicant's U.S. Pat. Nos. 5,040,963 and 5,221,507. The prior art mold 1 illustrated in FIG. 1 defines a common manifold arrangement 19 to convey both of the materials, which will form the preform, to the cavities 3. It is known in such an arrangement to repeatedly divide the material flow, whereby the flow path 33, 35, 37 from the material inlet 33 of the mold 1 to each cavity 3 is identical, whereby each cavity 3 will receive an equal metered amount of material at substantially the same temperature and at substantially the same time as every other cavity 3.
Construction details of the mold 1, its manifold system 19, the heating means 39 and the insulating means 41, together with the cavity design 3, 7 and cooling arrangements for the core pins 5 and cavities 3, the split neck rings 9, etc., are considered to be conventional in this technology and will be readily apparent to those skilled in the art. Similarly the plasticizer barrels 25 and 27 and ram pots 29 and 31 are of conventional construction, as are the general engineering details of the diverter valves 21 and 23. Accordingly these matters will not be described in detail in this application.
With reference now to FIG. 2, there is diagrammatically illustrates an interface between a first molten material 30 and a second molten material 32 in hot runner 33 at X (See FIG. 1). For the sake of illustration, it may be assumed that the first molten material 30 is supplied from plasticizer barrel 25 and the second molten material 32 is supplied from plasticizer barrel 27. When the diverter valves 21 and 23 have been operated to change the supply of molten material from plasticizer barrel 25 and ram pot 29 to molten material from plasticizer barrel 27 and ram pot 31, the second molten material is supplied sequentially behind and contiguously with the first molten material. Since the two materials are supplied sequentially and contiguously, an interface, as illustrated in FIG. 2, is formed between the two materials as they travel through the hot runners. The hot runner 33 is maintained at approximately 500.degree. F., and the frictional drag on the material is illustrated at the interface or melt front of the two materials.
The prior art injection molding techniques and manifold arrangements, however, have only been proposed for the production of preforms having multiple layers of different materials and have not been proposed for the molding of preforms having differently colored (including clear) areas for use in producing decorative containers. Until the recent invention, the process parameters for the injection of differently colored materials to produce multi-colored preforms and resulting containers were not understood.